Manually operable depth control for trenchers

Abstract

The invention relates to a mechanism permitting the manual control of an trencher which is normally carried in trailing relationship to a vehicle and is pivotally mounted to the vehicle. The effective cutting depth of this type trencher is determined by the angle of the frame carrying the endless chain relative to the horizontal. An upstanding sighting bar is pivotally mounted to the frame of the trencher and means are provided for maintaining the sighting bar in a true vertical position irrespective of the angle of the frame relative to the horizontal. Additionally, the effective vertical height of the sighting bar is varied as a trigonometric function of the angle of the digging frame relative to the horizontal.

I claim: 
     
       1. In a trencher of the type having an elongated digging frame having one end thereof pivotally mounted on a vehicle for movement in a vertical plane parallel to the path of movement of the vehicle, said digging frame having two spaced sprockets traversed by an endless chain carrying a plurality of spaced digging scoops, means on the vehicle for driving the forward sprocket and power means on the vehicle for varying the pivotal angle of said digging frame relative to the horizontal, thereby determining the depth of the trench being dug by said blades, the improvement comprising: 1. stationary sighting bar means disposed along the path of travel of the vehicle, said means defining a visual plane of known height relative to the desired depth of the trench to be dug;   2. an upstanding mast having its bottom end pivotally mounted on said digging frame adjacent the free end thereof for movement in a vertical plane;   3. means for maintaining said mast in a true vertical position irrespective of the angular position of said digging frame, said last mentioned means concurrently effecting a change in the effective height of said mast as a trigonometric function of the angle of said digging frame relative to the true horizontal and,   4. a horizontal sighting bar vertically ajustably mounted on said mast to permit said bar to be visually aligned with said stationary sighting bar means when said digging frame is initially forced into the ground to the desired starting depth for the trench to be dug.   
     
     
       2. The combination defined in claim 1 wherein said trigonometric function is equal to X 2  cos A + X 3  sin A, where A is the angle of the digging frame relative to the horizontal, X 2  is the perpendicular spacing between the mast pivot axis and the longitudinal axis of the digging frame, and X 3  is the spacing between the axis of the rear digging frame sprocket and the line defined by X 2 . 
     
     
       3. The combination defined in claim 1 wherein said mast position maintaining means comprises a vertical plate secured to said digging frame, said plate having a pair of cam slots therein respectively pivotally receiving a pair of vertically spaced horizontal pins traversing said mast. 
     
     
       4. In a trencher of the type having an elongated digging frame having one end thereof pivotally mounted on a vehicle for movement in a vertical plane parallel to the path of movement of the vehicle, said digging frame having two spaced sprockets traversed by an endless chain carrying a plurality of spaced digging scoops, means on the vehicle for driving the forward sprocket and power means on the vehicle for varying the pivotal angle of said digging frame relative to the horizontal, thereby determining the depth of the trench being dug by said blades, the improvement comprising: 1. stationary sighting bar means disposed along the path of travel of the vehicle, said means defining a visual plane of known height relative to the desired depth of he trench to be dug;   2. s sub-frame mounted on said digging frame in cantilevered over-lying relationship thereto, the free end of said sub-frame over-lying the position of said rear sprocket;   3. an upstanding plate secured to the free end of said sub-frame;   4. an upstanding mast having a bifurcated bottom end portion straddling said plate and supported thereby for both limited pivotal movement in a vertical plane and concurrent vertical movement;   5. cam means on said plate for varying the effective height of said mast as a trigonometric function of said pivotal angle of said digging frame;   6. a horizontal sighting bar vertically adjustably mounted on the top of said mast to permit manual alignment of said sighting bar with said stationary sighting bar means when said digging frame is initially positioned at the desired trench depth, and   7. means for maintaining said mast in a true vertical position irrespective of the angular position of the digging frame.   
     
     
       5. The combination defined in claim 4 wherein said cam means comprises two vertically spaced slots in said plate respectively trasversed by two verticlly spaced horizontal pins passing through the bifurcated bottom portions of said mast.